EP 0 321 809 B1 has disclosed a conical burner comprising a plurality of shells, known as a double-cone burner. The conical swirl generator, which is composed of a plurality of shells, generates a continuous swirling flow in a swirl space, which on account of the swirl increasing in the direction of the combustion chamber becomes unstable and changes into an annular swirling flow with backflow in the core. The shells of the swirl generator are assembled in such a manner that tangential air inlet slots for combustion air are formed along the burner axis. Feeds for the premix gas, i.e. the gaseous fuel, which have outlet openings for the premix gas distributed along the direction of the burner axis, are provided at these air inlet slots at the leading edge of the cone shells. The gas is injected through the outlet openings or bores transversely with respect to the air inlet gap. This injection, in conjunction with the swirl of the combustion air/fuel gas flow generated in the swirl space, leads to thorough mixing of the combustion or premix gas with the combustion air. Thorough mixing is a precondition in these premix burners for lower NOx emissions during combustion.
To further improve a burner of this type, EP 0 780 629 A2 has disclosed a burner for a heat generator which, following the swirl generator, has an additional mixing section for further mixing of fuel and combustion air. This mixing section may, for example, be designed as a section of tube which is connected downstream and into which the flow emerging from the swirl generator is transferred without significant flow losses. The additional mixing section makes it possible to further increase the degree of mixing and therefore to further lower the pollutant emissions.
WO 93/17279 has described a further known premix burner, in which a cylindrical swirl generator with a conical inner body is used. In the case of this burner, the premix gas is likewise injected into the swirl space via feeds with corresponding outlet openings which are arranged along the axially running air inlet slots. In the conical inner body, the burner additionally has a central feed for fuel gas, which can be injected into the swirl space close to the burner outlet for pilot control. The additional pilot stage is used to start up the burner and to widen the operating range.
EP 1 070 915 A1 has disclosed a premix burner in which the fuel gas supply is mechanically decoupled from the swirl generator. As a result, when fuel gases that have not been preheated or have been only slightly preheated are used, stresses caused by thermal expansions are avoided. In this case, the swirl generator is provided with a row of openings, through which fuel lines for gas premix operation, which are mechanically decoupled from the swirl generator, project into the interior of the swirl generator, where they supply gaseous fuel to the swirled-up flow of combustion air.
These known premix burners of the prior art are what are known as swirl-stabilized premix burners, in which a fuel mass flow, prior to combustion, is distributed as homogeneously as possible in a combustion air mass flow. In these types of burners, the combustion air flows in via tangential air inlet slots in the swirl generators. The fuel, in particular natural gas, is typically injected along the air inlet slots.
In gas turbines, in addition to natural gas and liquid fuel, generally diesel oil or Oil#2, in recent times synthetically produced gases, known as Mbtu and Lbtu gases, also have been used for combustion. These synthesis gases are produced by the gasification of coal or oil residues. They are characterized by mostly comprising H2 and CO. In addition, there is a smaller proportion of inert constituents, such as N2 or CO2.
In the case of the combustion of synthesis gas, the injection which has proven successful for natural gas in burners of the prior art cannot be retained, on account of a high risk of flashback.
This results in the following peculiarities and requirements in a burner that is to be operated with synthesis gas as distinct from a burner using natural gas. Depending on the dilution of the synthesis gas, which is known per se from the prior art, synthesis gas requires a fuel volumetric flow which is around four times—and in the case of undiluted synthesis gas up to seven times or even more—higher than comparable natural gas burners, so that with the same gas holes in the burner, significantly different pulse ratios result. On account of the high hydrogen content in the synthesis gas, and the associated low ignition temperature and high flame velocity of the hydrogen, the fuel is highly reactive, so that in particular the flashback characteristics and the residence time of ignitable fuel-air mix in the vicinity of the burner need to be investigated. Furthermore, stable and safe combustion of synthesis gases for a sufficiently wide range of calorific values has to be ensured, despite the synthesis gas having different compositions depending on the process quality of the gasification and starting product, for example oil residues. In order, under these conditions, nevertheless to achieve premixing and therefore the typical lower emissions during combustion, these synthesis gases are generally diluted with the inert constituents N2 or steam prior to combustion. Moreover, this improves the stability of combustion and in particular reduces the risk of flashback which is inherent to the high H2 content. Therefore, the burner has to be able to safely and stably burn synthesis gases of different compositions, in particular of different dilutions.
Furthermore, it is advantageous if, in addition to the synthesis gas, the burner can also safely burn a reserve fuel, known as a back-up fuel. In the case of the highly complex integrated gasification combined cycle (IGCC) installation, this requirement results from the demand for high availability. In such a situation, the burner should function safely and reliably even in mixed operation using synthesis gas and back-up fuel, for example diesel oil, while maximizing the fuel mix spectrum that can be used for burner operation in mixed operation of an individual burner. Of course, low levels of emissions (NOx≦25 vppm, CO≦5 vppm) should be ensured for the fuels which are specified and used.
EP 0 610 722 A1 has disclosed a double-cone burner, in which a group of fuel outlet openings for a synthesis gas are arranged at the swirl generator, distributed around the burner axis, at a combustion chamber-side end of the burner. These outlet openings are supplied via a separate fuel line and allow the burner to operate with undiluted synthesis gas.
Working on the basis of this prior art, the present invention relates to a burner which ensures safe and stable combustion both for undiluted synthesis gas and for dilute synthesis gas and moreover has a long service life. The burner should in particular satisfy the requirements listed above and, in preferred refinements, should allow operation with a plurality of types of fuel, including in mixed operation.